Modification of polymers using multilayered “smart pellet” additives: Part II

A magnesium-based inorganic whisker was compounded with polypropylene and with polysulfone (FP/PP and FPSF/PP^*, respectively) and then multilayered into alternating structures with unfilled polypropylene (PP). These multilayered materials were cut into FP/PP and FPSF/PP^* “smart pellets”, which were then added to polypropylene matrix polymer as masterbatches to deliver potential reinforcement to injection molded parts. The morphologies of both the smart pellets and the composites produced with them were studied by scanning electron microscopy (SEM). The inorganic whiskers were found to be aligned in the machine direction in the smart pellets. Mechanical properties of the composites were investigated by performing tensile, flexural, and impact strength tests. Inorganic whiskers combined with PSF offered higher flexural modulus in comparison to those via conventional blending; no significant improvement was observed in tensile modulus or impact strength of these composites.     

Lignocellulosic flour‐reinforced poly(hydroxybutyrate‐co‐valerate) composites

Residual lignocellulosic flour from spruce and ground olive stone was used as a natural filler in poly(hydroxybutyrate‐co‐valerate) (PHBV)‐based composites. The morphology and the thermal properties of these composites were investigated by scanning electron microscopy and differential scanning calorimetry, respectively. Lignocellulosic fillers acted as nucleating sites for the crystallization of PHBV and strongly enhanced its degree of crystallinity. Dynamic mechanical analysis and tensile properties of these materials were also studied. A significant reinforcing effect was displayed by dynamic mechanical analysis at temperatures higher than the glass–rubber transition of the matrix. In addition, for low‐particle‐size spruce, a stabilization of the modulus was observed up to 500 K. High‐strain tensile properties did not show any reinforcing effect. This apparent disagreement was explained by the poor adhesion between the hydrophilic lignocellulosic filler and the hydrophobic polymeric matrix. To validate this hypothesis, the experimental data were compared with predicted data involving the percolation concept. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1302–1315, 2003     

Mechanical and thermal properties of waterborne epoxy composites containing cellulose nanocrystals

Cellulose nanocrystals (CNCs) are reinforcing fillers of emerging interest for polymers due to their high modulus and potential for sustainable production. In this study, CNC-based composites with a waterborne epoxy resin matrix were prepared and characterized to determine morphology, water content, and thermal and mechanical properties. While some CNC aggregation was observed, the glass transition temperature (T_g) and modulus for the composites increased with increasing CNC content. Relative to neat epoxy, at 15 wt.% CNC the storage modulus increased by 100%, the T_g increased from 66.5 °C to 75.5 °C, and tensile strength increased from 40 MPa to 60 MPa, suggesting good adhesion between epoxy and CNC surfaces exposed to the matrix. Additionally, no additional water content resulting from CNC addition were observed. These results provide evidence that CNCs can improve thermomechanical performance of waterborne epoxy polymers and that they are promising as reinforcing fillers in structural materials and coatings.     

Polymerization compounding composites of nylon‐6,6/short glass fiber

Nylon‐6,6 was grafted onto the surface of short glass fibers through the sequential reaction of adipoyl chloride and hexamethylenediamine onto the fiber surface. Grafted and unsized short glass fibers (USGF) were used to prepare composites with nylon‐6,6 via melt blending. The glass fibers were found to act as nucleating agents for the nylon‐6,6 matrix. Grafted glass fiber composites have higher crystallization temperatures than USGF composites, indicating that grafted nylon‐6,6 molecules further increase crystallization rate of composites. Grafted glass fiber composites were also found to have higher tensile strength, tensile modulus, dynamic storage modulus, and melt viscosity than USGF composites. Property enhancement is attributed to improved wetting and interactions between the nylon‐6,6 matrix and the modified surface of glass fibers, which is supported by scanning electron microscopy (SEM) analysis. The glass transition (tan δ) temperatures extracted from dynamic mechanical analysis (DMA) are found to be unchanged for USGF, while in the case of grafted glass fiber, tan δ increases with increasing glass fiber contents. Moreover, the peak values (i.e., intensity) of tan δ are slightly lower for grafted glass fiber composites than for USGF composites, further indicating improved interactions between the grafted glass fibers and nylon‐6,6 matrix. The Halpin‐Tsai and modified Kelly‐Tyson models were used to predict the tensile modulus and tensile strength, respectively.     

Reinforced polystyrene via solvent‐exfoliated graphene

Solvent‐exfoliated graphene (SEG)‐reinforced polystyrene (PS) composites were prepared using a straightforward solution‐casting method. SEG sheets, obtained by sonication‐assisted solvent direct exfoliation from natural graphite, were well dispersed in the PS matrix as evidenced from scanning electron microscopy and transmission electron microscopy observations. Addition of 0.5 wt% SEG resulted in a 6% increase in tensile strength and a 77% improvement in Young's modulus over pure PS due to the effective load transfer between SEG and PS matrix. The Young's moduli of the PS/SEG composites were obtained from both tensile experiments and calculations using the well‐established Halpin–Tsai model. Results from dynamic mechanical analysis indicated that the storage modulus of the PS/SEG composites was significantly improved relative to neat PS. The glass transition temperatures of the composites were found to increase substantially upon addition of SEG, consistent with differential scanning calorimetry analysis. © 2017 Society of Chemical Industry     

玻纤增强聚苯硫醚复合材料的增韧研究

针对玻纤增强聚苯硫醚材料韧性差的问题，对聚苯硫醚傲璃纤维复合体系的增韧进行了研究，考察了玻纤、改性聚合物、有机超细粒子对复合材料力学性能的影响。采用基体增韧（预增韧）与有机超细粒子增韧技术，在保持复合材料拉伸强度和模量的同时，较大地提高了冲击强度，获得了综合力学性能优异的纤维增强聚苯硫醚材料。     

Mechanical property and fracture morphology of fiber-reinforced polysulfone plasticized with acetylene-terminated sulfone

The mechanical property and fracture morphology of glass fiber- (GF) and carbon fiber- (CF) reinforced polysulfone (PSF) blends with bis (4-(4-ethynyl phenoxy) phenyl) sulfone (ATS-C) have been investigated. Experimental results show that the tensile and flexural properties and impact strength of GF-reinforced ATS-C/PSF composites decrease as the processing temperature or/and the processing time increase, but CF-reinforced ATS-C/PSF composites exhibit better mechanical properties. Although interlaminar shear strenght (ILSS) for fiber-reinforced ATS-C/PSF composites decreases, scanning electron microscopy (SEM) observation of fracture surface indicates that the fractural model of fiber-reinforced PSF composites changes from the interfacial debonding fracture to the matrix fracture at the interfacial region with addition of ATS-C and the increase of the processing temperature. The end-use temperature of polysulfone can be retained and solvent resistance of polysulfone can be improved due to the formation of a semi-interpenetrating polymer network. © 1994 John Wiley & Sons, Inc.     

Self‐crosslinkable lignin/epoxidized natural rubber composites

Self‐crosslinkable lignin/epoxidized natural rubber composites (SLEs) were prepared through a high‐temperature dynamic heat treatment procedure followed by a postcuring process. Because of the ring‐opening reaction between lignin and epoxidized natural rubber (ENR), lignin as a crosslinker and reinforcing filler was uniformly dispersed into the ENR matrix and was highly compatible with the polymer matrix; this was confirmed by scanning electron microscopy. The curing behavior, mechanical properties, and dynamic mechanical properties of the SLEs were studied. The results show that the crosslinking degree, glass‐transition temperature, modulus, and tensile properties of the SLEs substantially increased with the addition of lignin. A physical model was used to verify the strong interactions between lignin and ENR. Stress–strain curves and X‐ray diffraction suggested that the reinforcement effect on the SLEs mainly originated from lignin itself rather than from strain‐induced crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41166.     

The Mechanical Properties and Chemical Resistance of Short Glass-Fiber-Reinforced Epoxy Composites

ABSTRACT

Epoxy–short glass fiber composites were prepared by directly blending two-pack system of Araldite (CY-230) and hardner (HY-951) with short glass fibers. The short glass fiber content was varied from 2% to 10% by weight of the total matrix. These composites were then characterized for morphology using scanning electron microscopy, mechanical properties, that is, tensile and flexural properties and resistance toward various chemicals. The epoxy-glass fiber composites showed improved tensile and flexural properties but increased dispersion among the properties with increasing fiber content. Several reasons to explain these effects in terms of reinforcing mechanisms were discussed. These composites were stable in most chemicals but were completely destroyed in concentrated sulfuric acid, nitric acid, and pyridine.     

Effect of a dodecylsulfate‐modified magnesium–aluminum layered double hydroxide on the morphology and fracture of polystyrene and poly(styrene‐co‐acrylonitrile) composites

Composites of polystyrene (PS) and poly(styrene‐co‐acrylonitrile) (SAN) containing a fraction of a dodecylsulfate‐modified Mg–Al layered double hydroxide (LDH) were prepared by means of a melt‐extrusion process. The structure and morphology were analyzed with wide‐angle X‐ray scattering and transmission electron microscopy, respectively. The X‐ray spectra of the PS matrix composite displayed the diffraction peak characteristic of the hybrid LDH basal plane at 2θ = 3.1 deg. The SAN matrix composite did not exhibit such a diffraction peak. Both PS and SAN composites displayed an intercalated type of morphology with respect to the LDH platelets, as assessed by transmission electron microscopy. A plasticizing effect due to the hybrid LDH particles was observed for all composites and was supported by a decrease in the glass‐transition temperature values and by Fourier transform infrared spectra. Besides tensile properties, the fracture toughness of the composites was compared with that of the pure polymers through the linear elastic fracture mechanics parameters. They were determined from fracture tests under a three‐point‐bending configuration. The results indicated that the effect of adding a small fraction of modified LDH particles to SAN caused an improvement in fracture toughness of 50% with respect to that of the pure polymer. Moreover, the relative increase in the fracture energy was about 200%. For PS matrix composites, both tensile properties and linear elastic fracture mechanics fracture parameters remained unaffected. These results were explained on the basis of the different plasticities developed by both polymers around the particles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ionomer. I. The effect of woven glass mat reinforcement on tensile properties

An investigation was conducted on ionomer polymer. The ionomer pellets were molded into a thin sheet before fabrication into composites. The reinforcing agent used was woven glass mat. Before fabrication, the woven glass mat was treated with the following: 1. silane coupling agent for 5 min and dried at room temperature; 2. silane coupling agent for 5 min and dried in the oven at 110°C for 15 min; 3. Ultraviolet radiation for 5 min; and 4. silane (oven dried + ultraviolet). The composites were fabricated at various pressure, time, and temperature. An ideal processing condition was established, i.e., pressure = 5 MPa, temperature = 180°C, and the impregnation time = 30 min. The void contents of the composites were estimated using the ignition method and the tensile properties were measured. The results revealed that good impregnation of the matrix ionomer into the reinforcing agent can be achieved at 180°C. This was confirmed by low void content as compared with other test temperatures. Further clarification was through the tensile properties, which were higher than those at lower temperatures (120 and 150°C). The effect of fiber orientation was checked, and both 0 and 90° had identical strengths and moduli irrespective of the various fiber treatments. Apart from the void contents, the degree of impregnation was also checked based on the tensile strengths in 45, 25, and 60° fiber orientations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1395–1400, 2001     

Effect of macromolecular coupling agent on the property of PP/GF composites

Silane‐grafted polypropylene manufactured by a reactive grafting process was used as the coupling agent in polypropylene/glass‐fiber composites to improve the interaction of the interfacial regions. Polypropylene reinforced with 30% by weight of short glass fibers was injection‐molded and the mechanical behaviors were investigated. The results indicate that the mechanical properties (tensile strength, tensile modulus, flexural strength, flexural modulus, and Izod impact strength) of the composite increased remarkably as compared with the noncoupled glass fiber/polypropylene. SEM of the fracture surfaces of the coupled composites shows a good adhesion at the fiber/matrix interface: The fibers are coated with matrix polymer, and a matrix transition region exists near the fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1537–1542, 1999     

Sheet extrusion of microcomposites based on thermotropic liquid crystalline polymers and polypropylene

This work is concerned with the extrusion of sheets from pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The TLCPs used were HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties for in situ composites in which the TLCP fibrils are generated in contractions in the die and the subsequent drawing step. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors affecting the mechanical properties of the composite sheets considered include the effect of in situ composite strand properties and TLCP concentration. In addition, the properties of the extruded sheets are compared to those of microcomposites processed by means of injection molding. It is shown that the sheets produced using microcomposites have a good balance between the machine and transverse direction properties (ratios of these properties ranging from 0.8 to 1.2) and those properties compare well to those obtained by processing microcomposites in injection molding. The tensile modulus of the composite sheets increases with increasing in situ composite strand modulus. The moduli of the 20 wt% Vectra A950 and HX6000 composites are about equal to the modulus of 20 wt% glass reinforced PP (about 2.1 GPa), while the tensile strength of the TLCP reinforced composites is 28% lower than that of the glass reinforced PP. Furthermore, it is shown that the tensile modulus of the 10 wt% TLCP composites approach the predictions of composite theory, while at 20 and 30 wt% TLCP negative deviations from the predictions of composite theory are seen. Finally, it is concluded that the properties of the sheets produced through the extrusion of microcomposites may be further improved by improving the modulus of in situ composite strands and reducing the TLCP fiber diameter.     

Recycling of poly(ethylene terephthalate) as polymer‐polymer composites

Microfibrillar reinforced composites (MFC) comprising an isotropic matrix from a lower melting polymer reinforced by microfibrils of a higher melting polymer were manufactured under industrially relevant conditions and processed via injection molding. Low density polyethylene (LDPE) (matrix) and recycled poly(ethylene terephthalate) (PET) (reinforcing material) from bottles were melt blended (in 30/70 and 50/50 PET/LDPE wt ratio) and extruded, followed by continuous drawing, pelletizing and injection molding of dogbone samples. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), dynamic mechanical thermal analysis (DMTA), and mechanical testing. SEM and WAXS showed that the extruded blend is isotropic but becomes highly oriented after drawing, being converted into a polymer‐polymer composite upon injection molding at temperatures below the melting temperature of PET. This MFC is characterized by an isotropic LDPE matrix reinforced by randomly distributed PET microfibrils, as concluded from the WAXS patterns and SEM observations. The MFC dogbone samples show impressive mechanical properties—the elastic modulus is about 10 times higher than that of LDPE and about three times higher than reinforced LDPE with glass spheres, approaching the modulus of LDPE reinforced with 30 wt% short‐glass fibers (GF). The tensile strength is at least two times higher than that of LDPE or of reinforced LDPE with glass spheres, approaching that of reinforced LDPE with 30 wt% GF. The impact strength of LDPE increases by 50% after reinforcement with PET. It is concluded that: (i) the MFC approach can be applied in industrially relevant conditions using various blend partners, and (ii) the MFC concept represents an attractive alternative for recycling of PET as well as other polymers.     

Temperature dependence of reinforcement in the composites polyurethane rubber–crosslinked polymeric filler

The temperature dependence of the components of the complex tensile and shear modulus of composites thermoplastic polyurethane rubber (Estan 5707)–crosslinked polymeric filler has been determined using torsional pendulum and Rheovibron viscoelastometer techniques. For comparison, dynamic mechanical properties of the system Estan 5707–glass beads were determined. The temperature dependence of the relative modulus (modulus of composite/modulus of matrix) of the former composites exhibited a pronounced maximum at about 50°C above the glass transition temperature of the matrix. This maximum of reinforcement was discussed in terms of (a) immobilized interfacial layer, (b) broadening of the spectrum of relaxation times, and (c) increase in the glass transition temperature of the matrix. From the excess reinforcement, i.e., the discrepancy between experimental data and theoretical prediction, an apparent thickness of the immobilized layer was calculated.     

Investigation of mechanical properties of alumina nanoparticle‐loaded hybrid glass/carbon‐fiber‐reinforced epoxy composites

This research work investigates the tensile strength and elastic modulus of the alumina nanoparticles, glass fiber, and carbon fiber reinforced epoxy composites. The first type composites were made by adding 1–5 wt % (in the interval of 1%) of alumina to the epoxy matrix, whereas the second and third categories of composites were made by adding 1–5 wt % short glass, carbon fibers to the matrix. A fourth type of composite has also been synthesized by incorporating both alumina particles (2 wt %) and fibers to the epoxy. Results showed that the longitudinal modulus has significantly improved because of the filler additions. Both tensile strength and modulus are further better for hybrid composites consisting both alumina particles and glass fibers or carbon fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39749.     

Effect of compounding on the properties of short fiber reinforced injection moldable thermoplastic composites

The mechanical properties of short-fiber-reinforced thermoplastic composites depend on the degree of interfacial bond strength between the fibers and polymer matrix. This interfacial bond strength can be increased by appropriate coupling agents. This study shows, for example, that an amino silane coupling agent improves the bond strength of nylon-aluminum fiber composites, but not polycarbonate-aluminum fiber composites. For cases where appropriate coupling agents are not available it is important to maintain as high a fiber aspect ratio as possible in a molded part. This study shows that a single screw compounder does less damage to glass or carbon fibers than a twin screw compounder under similar processing conditions when the polymer is in the form of pellets. When the polymer is supplied as a powder, satisfactory dry blends can be produced and the twin screw compounder does less damage to the fibers. In both cases, however, fibers initially 6 mm long are reduced to an average length less than 0.5 mm. The greatest degree of fiber size retention was observed when extrusion coated fiber pellets were used in the injection molding machine. The relationship between a fiber's tensile strength and the interfacial shear strength between a fiber and matrix yields a critical fiber aspect ratio below which the maximum reinforcing capability of the fibers are not being utilized. For the polymers investigated in this program, the critical aspect ratio for carbon fibers was found to be between 16 and 25 to 1. The polymers investigated include flame-retardant grades of acrylonitrile-butadiene-styrene (ABS) and poly(phenylene oxide)/polystyrene blend, nylon 6/6 and poly(phenylene sulfide).     

Jatropha deoiled cake filler‐reinforced medium‐density polyethylene biocomposites: Effect of filler loading and coupling agent on the mechanical,dynamic mechanical and morphological properties

This work focuses on the performance of Jatropha deoiled cake (JOC) as filler for medium‐density polyethylene. The biocomposites were prepared using a melt‐compounding technique. Maleated polyethylene (MPE) was used as a reactive additive to promote polymer/filler interfacial adhesion. The mechanical, thermodynamic mechanical and morphological properties of the resultant composites were investigated. The results show that the incorporation of JOC into the matrix reduced tensile, flexural, and impact strengths compared with the pure matrix. Moreover, tensile and flexural moduli were increased. The composites prepared with MPE had better mechanical properties and lower water uptake, indicating an enhancement in the interfacial interaction between JOC and polyethylene systems. The storage modulus was increased by the increase in filler loading and decreased when MPE was used. The composites loss modulus curves revealed two glass transitions indicating partial miscible blends. Scanning electron microscopy analysis for maleated composites showed a relatively homogeneous morphology with few left cavities, and the filler particle size is smaller compared to nontreated composites. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Microcrystalline cellulose as reactive reinforcing fillers for epoxidized soybean oil polymer composites

Microcrystalline cellulose (MCC) and its oxidized product dialdehyde cellulose (DAC) were introduced as the reinforcing filler in epoxidized soybean oil (ESO) thermosetting polymer. The composites comprising up to 25 wt % cellulose fillers were obtained via a solution casting. The reinforcing effects of the cellulose were evaluated by microstructure analysis, dynamic mechanical analysis, and tensile and thermal stability tests. The results showed that at the same filler concentration, DAC led to higher stretching strength, modulus, and break elongation than MCC. The 5 wt % DAC loading in ESO polymer exhibits the highest toughness and thermal stability due to the good dispersion and interfacial interaction between DAC and ESO polymer matrix. The increased storage modulus and glass transition temperature also indicate the cellulose fillers impart stiffness to the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42488.     

Surface‐modified talc particles by acetoxy groups grafting: Effects on mechanical properties of polypropylene/talc composites

This article deals with the effects of surface‐modified talc particles on mechanical properties of polypropylene (PP)/talc composites. These materials were prepared by injection molding of PP blended with different concentrations of nontreated and treated talc, under the same processing conditions. Differential thermal calorimetry and scanning electron microscopy were used to assess thermal properties and morphology of the final composites. The reinforcing effect of talc, either treated or nontreated surface, on PP is analyzed through the tensile properties as a function of the mineral content (0–10 wt%). Morphological structure of composites revealed that the talc treatment improved the particle dispersion and distribution within the PP matrix and enhanced the interfacial PP‐talc adhesion. The mechanical properties of these composites, especially the Young modulus, tensile strength and elongation at break, were found to be improved respect to PP‐untreated talc ones. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers